Method trunc

crates/rustc_codegen_spirv/src/builder/builder_methods.rs:1400–1402

intcast has the logic for dealing with bools, so use that

(&mut self, val: Self::Value, dest_ty: Self::Type)

    // intcast has the logic for dealing with bools, so use that
    fn trunc(&mut self, val: Self::Value, dest_ty: Self::Type) -> Self::Value {
        self.intcast(val, dest_ty, false)
    }
    fn sext(&mut self, val: Self::Value, dest_ty: Self::Type) -> Self::Value {
        self.intcast(val, dest_ty, true)
    }